Radio frequency (RF) spectrum is a valuable commodity in today's world. There are more people desiring to use the RF spectrum than there is spectrum to go around, so use of the spectrum must be regulated. In many countries, the RF spectrum is regulated by governmental bodies. The Federal Communications Commission (FCC) regulates the RF spectrum in the United States.
The RF spectrum is regulated usually in one of two ways. A first way that governmental bodies regulates the RF spectrum is to sell portions of it to the highest bidder. The winning bidder, then has exclusive use of the particular portion of the RF spectrum that he has just purchased. This is way that RF spectrum for cellular telephones, television and radio channels are allocated. Single user allocations are the preferred method for applications where interference from other sources cannot be tolerated.
A second way that the government regulates RF spectrum usage is to create certain bands where anyone can use the RF spectrum as long as they comply with specified spectrum usage rules. For example, in the United States, the FCC has created three such bands. These bands are called the industrial, scientific, and medical (ISM) and the unified national information infrastructure (UNII) bands and are in the 900 MHz, 2.4 GHz, and 5.7 GHz portions of the RF spectrum. Anyone may use the spectrum in these bands as long as they are able to accept interference from other users and do not cause undue interference to other users.
The ISM and UNII bands have created a huge market for wireless consumer electronics products, such as cordless telephones, wireless computer products, and wireless computer networks. However, the popularity of the bands has resulted in a problem that many product developers did not anticipate, namely, performance degradation due to inter-product interference.
In wireless computer networks, the performance degradation is seen mainly in the network's data transfer rates. A wireless network today is capable of delivering a data transfer rate of 11 Mbps or more in an interference free environment, but if interference is introduced, the data transfer rate may drop to only a small fraction of the maximum.
Interference to a wireless computer network may come from many different forms. Sources of interference may include large appliances in the environment, other electronic devices such as pagers, cordless telephones, and microwave ovens, and other wireless computer networks. The relatively simple sources of interference such as appliances and pagers and telephones are relatively simple to deal with because their interference is periodic and is usually predictable. Because the interference is predictable, it is usually easy to avoid.
When multiple wireless computer networks are collocated, the wireless networks may interfere with one another. If the wireless computer networks are of the same type (the networks use a common technical standard), then there are often built-in mechanisms that permit the networks to remain operating at near optimal levels. However, if the wireless computers networks are of differing types, then there normally no built-in techniques that will permit the networks to work around each other.
Interference from wireless networks are more difficult to deal with due to the bursty nature of computer traffic and the fact the networks are often adaptive and can adjust their behavior depending on network conditions. The adaptive behavior often makes the interference worse because in many cases the network simply increases its transmission power when it detects a decrease in data rate. The increased transmission power results in a corresponding increase in the interference to other networks.
The collocation problem is at its worst when a single device has wireless network cards for multiple wireless networks installed. For example, a personal computer may have two (or more) wireless network interface cards installed inside it. A first card may be used with an IEEE 802.11 (802.11) wireless Ethernet network that permits the personal computer access to a company's corporate intranet and access to the Internet. A second card may be used with a Bluetooth (BT) network that permits the personal computer short-range access to personal digital assistants, printers, cellular telephones, etc.
Unfortunately, since the two network cards are often only a few inches (or less) from one another, when one card transmits, it often saturates the receiver of the other. This prevents the other card from receiving any information transmitted in its own network. A similar problem occurs when one card is receiving information, where the received information from one network may be so powerful that it obliterates any information intended for the other network.
One proposed solution for the collocation of multiple wireless computer networks in a single device involves regulating traffic flow from the networks with fixed priorities. This involves assigning different traffic classes in each of the networks a different priority and then allowing the traffic classes with higher priorities to transmit at the expense of lower priority traffic. However, with a fixed priority structure, it is very possible to have the higher priority traffic dominate access to the networks and starve the lower priority traffic. Additionally, by using fixed priorities, it is not possible to adjust the priorities to meet changing network conditions.
A need has therefore arisen for a solution that allows multiple wireless computer networks to collocate and at the same time, permit sufficient flexibility so that the solution itself may be adjusted to meet changing network conditions.